1. Field of the Invention
The present invention relates to an annular clutch seal which is interposed between a clutch plate in a dry clutch and a piston pressing the clutch plate. The clutch seal of the present invention is employed, for example, in a hybrid driving force transmission device and an automatic transmission of a vehicle such as a motor vehicle.
2. Description of the Conventional Art
There has been conventionally known a clutch seal 54 which is an annular seal 54 interposed between a clutch plate 52 in a dry clutch 51 and a piston 53 pressing the clutch plate 52, has a middle ring 58 fixed to the piston between an outer ring 56 and an inner ring 57 which are fixed to a clutch housing 55, and has membrane portions 59 and 60 constructed by a rubber-like elastic body respectively between the outer ring 56 and the middle ring 58 and between the inner ring 57 and the middle ring 58, as shown in FIG. 5. The piston 53 moves rightward in the drawing by being pressed by a working fluid, turns on the clutch by pressing the clutch plate 52, and turns off the clutch by returning leftward. The seal 54 plays a role of sealing the working fluid so as to prevent the working fluid from entering into the clutch plate 52 side.
In the clutch seal 54, the membrane portions 59 and 60 constructed by the rubber-like elastic body elastically deform repeatedly according to a stroke action of the piston 53, and the membrane portions 59 and 60 are constantly exposed to a centrifugal force at the high-speed turning time. As a result, it is necessary to make an effect to enhance a durability of the membrane portions 59 and 60 as much as possible.
Further, in the case that the working fluid stands in concave surfaces of the membrane portions 59 and 60, the membrane portions 59 and 60 are abnormally deformed, generated strain becomes great, and the membrane portions 59 and 60 run into breakage. Therefore, it is important to prevent the working fluid from standing in the concave surfaces of the membrane portions 59 and 60.